The present invention relates to a seal device for providing a seal between two spaces having different pressures, and to a method for operating the same, and also relates to a substrate processing apparatus comprising a vacuum chamber. More specifically, the present invention relates to a non-contacting seal device capable of providing a suitable seal in a semiconductor manufacturing apparatus between two spaces having different pressures and method for operating the same, and also relates to a substrate processing apparatus comprising a vacuum chamber in which a stage device is provided, wherein a substrate for producing a semiconductor or a liquid crystal is loaded on the stage device and processed in the vacuum chamber. In the substrate processing apparatus of the present invention, the vacuum chamber is appropriately controlled so that a good vacuum environment produced in the vacuum chamber can be maintained.
Conventional non-contacting seal devices for providing a seal between spaces having different pressures are disclosed in U.S. Pat. Nos. 4,118,042, 4,191,385 and 4,425,508. The seal devices disclosed in the above documents are used in a clean environment, such as a vacuum environment, in which a movement (a rotary motion or a linear motion) of an object is effected. The purpose of using these seal devices is to effect a high-speed or smooth movement of the object without any risk of contamination of the clean environment.
Non-contacting seal devices tend to be used in the following two cases: when an object to be moved and a minimal structure are provided in a clean environment and a drive source and a guide mechanism for moving the object are provided outside the clean environment; and when a non-contact type bearing such as a static fluid bearing (e.g., an air bearing) is provided and a clean environment is sealed without reducing the merit of the non-contact type bearing. In the latter, (1) the static fluid bearing is provided within a clean environment, and the clean environment is sealed against fluid of the static fluid bearing, or (2) the bearing is provided outside a clean environment, and a non-contacting seal is provided between the clean environment and an external environment.
A characteristic of a non-contacting seal device is that it is able to separate two spaces in a non-contacting manner. In an individual apparatus to which a non-contacting seal device is applied (hereinafter, frequently referred to simply as “the apparatus”), such a characteristic of a non-contacting seal device is a merit when the seal device performs a sealing function in a normal operating condition. However, pressure conditions of the apparatus are subject to change at a time of starting or stopping the seal device or after stopping the seal device, depending on the method employed for operating the seal device. From the viewpoint of a time required for starting the individual apparatus, a risk of contamination when stopping the apparatus and maintaining a desired degree of cleanliness, it is necessary to take into account a way in which the apparatus is affected by the method for operating the seal device.
Referring to FIG. 1, explanation is made with regard to how the apparatus is affected by the method for operating the seal device, at the time of starting or stopping the seal device and after stopping the seal device. First, explanation is made with regard to the apparatus at the time of starting the seal device. As shown in FIG. 1, the seal device comprises a sealing passage 3 having a small cross-sectional area which connects a first space 1 and a second space 2. In an initial state, the first space 1, the second space 2 and the sealing passage 3 are maintained at the same pressure, for example, at atmospheric pressure. The first space 1 is a vacuum chamber which is to be brought into a high-vacuum condition for, for example, processing a substrate for manufacturing a semiconductor device. The second space 2 accommodates a transport mechanism for transporting substrates, and has a low degree of cleanliness as compared to the first space 1. The second space 2 may be an atmospheric environment in a clean room. In this state, the seal device is started. However, the following problems may arise, depending on the method used for starting the seal device.
[CASE 1]
In CASE 1, initially, a vacuum pump 41 in an evacuation line L1 is actuated and a valve 51 is opened, to thereby start evacuation through the evacuation line L1. Subsequently, a vacuum pump 42 in an evacuation line L2 is actuated and a valve 52 is opened, to thereby start evacuation through the evacuation line L2. In a normal operating condition of the seal device, the pressure relationship between the first space 1, the second space 2 and the sealing passage 3 is represented by P1<P3<P2 (in terms of a degree of vacuum, Vi>V3>V2), wherein P1, P2 and P3 represent the pressures in the first space 1, the second space 2 and the sealing passage 3, respectively, and V1, V2 and V3 represent the degrees of vacuum in the first space 1, the second space 2 and the sealing passage 3, respectively. In a transient state after the start of evacuation through the evacuation line L1 by opening the valve 51, the relationship P1<P3<P2 or P1<P3=P2 (for example, P1 is several Torr, P3 is a value between atmospheric pressure and several hundred Torr and P2 is atmospheric pressure) is established. In this state, a considerable amount of gas flows from the second space 2 into the first space 1.
Thereafter, when evacuation through the evacuation line L2 is started by opening the valve 52, most of the gas flowing from the second space 2 is introduced into the evacuation line L2 and does not flow into the first space 1. Consequently, the pressure relationship P1<P3<P2 in a normal operating condition (for example, P1 is 1E-6 Torr, P3 is 1E-3 Torr and P2 is atmospheric pressure) is established, and the seal device starts to operate in a normal operating condition.
Thus, in the above operation for starting the seal device, a considerable amount of gas flows from the second space 2 into the first space 1. Therefore, the degree of cleanliness of the first space 1 lowers. For example, when air having a humidity of 50% flows from the second space 2 into the first space 1, the ultimate degree of vacuum in the first space 1 lowers. Further, if the second space 2 contains foreign matter, such matter will enter a small gap in the sealing passage 3, and clog the sealing passage 3. The gap provided in the sealing passage 3 is generally 1 mm or less. Recently, a high-performance seal device adapted for sealing a gap as small as 0.005 mm (=5 μm) has also been made available.
[CASE 2]
In CASE 2, the vacuum pump 42 is first actuated and the valve 52 is opened, to thereby start evacuation through the evacuation line L2. Subsequently, the vacuum pump 41 is actuated and the valve 51 is opened, to thereby start evacuation through the evacuation line L1. The pressure relationship in a normal operating condition is P1<P3<P2 (in terms of a degree of vacuum, V1>V3>V2). In a transient state after the start of evacuation through the evacuation line L2 by opening the valve 52, the relationship P1>P3<P2 (for example, P1 is several hundred Torr, P3 is several Torr and P2 is atmospheric pressure) is established. Therefore, a gas flows from the second space 2 into the sealing passage 3.
Subsequently, evacuation through the evacuation line L1 is started by opening the valve 51. In this instance, a slight amount of gas flows from the second space 2 into the first space 1. Then, the pressure relationship in a normal operating condition, that is, P1<P3<P2 (for example, P1 is 1E-6 Torr, P3 is 1E-3 Torr and P2 is atmospheric pressure), is established, thus completing the starting operation. During the starting operation, there is a possibility that foreign matter contained in the second space 2 may become mixed in the gas flow and clog the small gap in the sealing passage 3.
Next, explanation is made with regard to problems arising due to a sequence of steps conducted for stopping the seal device. Initially, a differential exhausting sealing function is performed in a normal operating condition. The pressure relationship in this condition is P1<P3<P2 (in terms of a degree of vacuum, V1>V3>V2). For example, P1 is 1E-6 Torr, P3 is 1E-3 Torr and P2 is atmospheric pressure.
[CASE 3]
In CASE 3, the valve 51 and the valve 52 are closed at the same time. In this case, the first space 1 is subject to a phenomenon that a crack such as a sealing passage 3 is created in a wall defining a vacuum chamber. That is, a gas in the second space 2 vigorously flows through the sealing passage 3 into the first space 1. Thus, a considerable amount of gas flows from the second space 2 into the first space 1, thus lowering a degree of cleanliness of the first space 1. For example, when air having a humidity of 50% flows from the second space 2 into the first space 1, the ultimate degree of vacuum in the first space 1 lowers. Further, if the second space 2 contains foreign matter, such matter will enter a small gap in the sealing passage 3, and clog the sealing passage 3.
[CASE 4]
In CASE 4, the valve 52 is first closed, and then the valve 51 is closed. In this case also, the first space 1 is subject to a phenomenon that a crack such as a sealing passage 3 is created in a wall defining the vacuum chamber. That is, a gas in the second space 2 vigorously flows through the sealing passage 3 into the first space 1. This imparts to the vacuum pump 41, which draws a high vacuum in the first space 1, an effect similar to that of entry of the atmosphere. When use is made of a turbomolecular pump, of which turbine blades are rotated at ultrahigh speed and strike molecules, an excessive amount of external force acts on the blades, thus resulting in the possibility of breakage of the blades.
Thus, in CASE 4, a considerable amount of gas flows from the second space 2 into the first space 1, thus lowering the degree of cleanliness of the first space 1. For example, when air having a humidity of 50% flows from the second space 2 into the first space 1, the ultimate degree of vacuum in the first space 1 lowers. Further, if the second space 2 contains foreign matter, such matter will enter a small gap in the sealing passage 3, and clog the sealing passage 3.
[CASE 5]
When the valve 51 is first closed and the valve 52 is then closed, a considerable amount of gas flows from the second space 2 into the first space 1 through the gap in the sealing passage 3 until the pressure relationship P1 P3 or P1>P3 is established. Therefore, the degree of cleanliness of the first space 1 lowers. For example, when air having a humidity of 50% flows from the second space 2 into the first space 1, the ultimate degree of vacuum in the first space 1 lowers. Further, if the second space 2 contains foreign matter, such matter will enter a small gap in the sealing passage 3, and clog the sealing passage 3.
Next, explanation will be made with regard to how the apparatus is affected by the sealing passage 3 after stopping the seal device.
[CASE 6]
In each of CASES 3, 4 and 5, a gas flows from the second space 2 into the first space 1. If such a state is permitted, the first space 1 will be brought into a state similar to that of a vacuum chamber opened and exposed to a gas in an external environment, such as air in a clean room. In this case, if the air in a clean room is a moist gas having a humidity of about 50%, an inner surface of a wall defining the first space 1 is exposed to such a moist gas. Therefore, the ultimate degree of vacuum in the first space 1 when reproducing a vacuum becomes low. In other words, it is difficult to achieve the degree of vacuum for which the apparatus is set, and therefore the time for restarting the apparatus is markedly prolonged.
[CASE 7]
When dry gas is fed into the first space 1 in order to maintain the pressures in the first space 1 and the second space 2 at the same level, because the first space 1 and the second space 2 are communicated through the sealing passage 3, if the gas in the second space 2 has a high humidity, the humidity of the entire space including the first space 1 and the second space 2 moves towards a state of equilibrium. That is, the gas in the first space 1 acts like a dry sponge absorbing a water component of the gas occupying the second space 2. Consequently, water is adsorbed on the inner wall surface defining the first space 1. Therefore, the ultimate degree of vacuum in the first space 1 when reproducing a vacuum becomes low. In other words, it is difficult to achieve the degree of vacuum for which the apparatus is set, and therefore a time for restarting the apparatus is markedly prolonged.
After stopping the seal device, if the first space 1 is filled with air having a humidity of 50% and the apparatus is restarted 1 day after stopping of the seal device, an operation for reproducing a vacuum must be conducted for 1 month to achieve a set degree of vacuum in the first space 1.
Generally, in a substrate processing apparatus, a substrate is loaded on a stage device, and moved so that a specific region on the substrate's surface is located at a predetermined position and processed.
The stage device includes a movable base and a stationary base, and a guide element and a drive element. To move a substrate loaded on the movable base, a control command is applied to the drive element, which imparts a thrust force to the movable base. Thus, the movable base is moved, while being guided by the guide element.
As a guide element, a rolling guide element has been conventionally used. The rolling guide element requires use of a lubricant, and an effective means to suppress generation of dust and a release of gas accompanying a rolling motion of the guide element is studied.
As a drive element, a rotary motor or a linear motor, which converts electric energy to kinetic energy, is employed. A rotary motor is used in combination with a magnetic fluid seal. This combination has a merit such that the motor can be provided outside a vacuum chamber in which a substrate is provided. That is, the motor can be used in an atmospheric environment, and the type of the motor can therefore be selected from a wide range.
However, the use of a rotary motor in combination with a magnetic fluid seal has a demerit such that (a) the life of the magnetic fluid seal becomes short. The life of the magnetic fluid seal is in inverse proportion to the degree of vacuum. That is, the higher the degree of vacuum created in the vacuum chamber, the shorter the life of the magnetic fluid seal. Another demerit is that (b) it is essential to provide a mechanism for converting a rotary motion to a linear motion. Thus, it is not possible to effect a smooth linear motion due to rattling or friction of the converting mechanism.
Therefore, in recent years, there has been an increasing tendency to use a linear motor, which does not require use of a converting mechanism, and therefore has no demerit (b). However, there is no vacuum seal suitable for use with a linear motor. Therefore, it has been desired to employ a linear motor which can be suitably used within a vacuum environment, that is, one which is free from problems, such as (c) a release of gas, (d) generation of heat and (e) generation of dust. However, the problems of a release of gas and generation of heat cannot be completely avoided in practice. Therefore, a conventional substrate processing apparatus such as that shown in FIG. 2 is employed.
In FIG. 2, reference 1a denotes a first space or vacuum chamber; 2 a second space or vacuum chamber; 4 a housing defining the first and second vacuum chambers 1 and 2; 3a a passage formed by a wall 6 between the first vacuum chamber 1 and the second vacuum chamber 2; 11 a stage device provided in the first vacuum chamber 1 and comprising a stationary base 12 and a movable base 13 movably supported on the stationary base 12 by a rolling mechanism 14; 15 a drive device provided in the second vacuum chamber 2 and connected to the movable base 13 through a connecting member 16 extending through the passage 3a; and 17 an electron beam generating column for processing a substrate S loaded on the movable base 13. The passage 3a provides a restricted portion which connects the first space or vacuum chamber 1a and the second space or vacuum chamber 2a. The first vacuum chamber 1a and the second vacuum chamber 2a are evacuated by means of individual vacuum pumps 18 and 19, such as ion pumps. The pressure in the first vacuum chamber 1a and the pressure in the second vacuum chamber 2a are controlled so as to satisfy the relationship P1<P2<P0, wherein P1 and P2 represent the pressure in the first vacuum chamber 1a and the pressure in the second vacuum chamber 2a, respectively, and P0 represents atmospheric pressure. (If P1, P2 and P0 are replaced by the corresponding degrees of vacuum DV1, DV2 and DV0, the relationship DV1>DV2>DV0 is established.) The purpose of this arrangement is to protect the first vacuum chamber 1a from gas, heat and dust generated from the drive element. It should be noted that in the present specification, the term “a vacuum chamber” does not mean a chamber in an absolute vacuum, but rather a chamber having a low pressure such as that which is referred to as a “vacuum” in the related art.
FIG. 3 shows another example of a conventional substrate processing apparatus. In FIG. 3, the same parts or portions as those shown in FIG. 2 are designated by the same reference numerals as used in FIG. 2, and explanation thereof is omitted. In the substrate processing apparatus in FIG. 3, a bellows type seal device 21 is provided in a passage 5 which corresponds to the passage 3a forming the restricted portion in FIG. 2, so as to prevent a flow of gas from the second vacuum chamber 2a to the first vacuum chamber 1a. However, a reaction force and vibrations produced by expansion and contraction of the bellows interfere with a smooth movement of a substrate. This can be avoided by using a fluorine resin, which is flexible and can be suitably used in a vacuum condition, for the bellows. When a difference between the pressures P1 and P2 is small, even a bellows made of a flexible material is capable of serving as a pressure bulkhead.
FIG. 4 shows a further example of a conventional substrate processing apparatus. In FIG. 4, the same parts or portions as those shown in FIGS. 2 and 3 are designated by the same reference numerals as used in FIGS. 2 and 3, and explanation thereof is omitted. In the substrate processing apparatus of FIG. 4, the second space is changed from a vacuum chamber 2a shown in FIG. 2 to an atmospheric environment under atmospheric pressure P0 in which the drive device 15 (such as a linear motor) is disposed. Since the second vacuum chamber 2a is replaced with an atmospheric environment, the bellows type seal device 21 which also serves as a pressure bulkhead is required to withstand a differential pressure as high as 1 kg/cm2. Therefore, a bellows made of a flexible material such as a fluorine resin cannot be used, and effects of a reaction force and vibrations produced by a bellows cannot be avoided. However, a countermeasure for generation of heat by the drive element (i.e., cooling) can be easily taken, and a vacuum system having a simple construction can be employed.
FIG. 5 shows a further example of a conventional substrate processing apparatus. In FIG. 5, the same parts or portions as those shown in FIGS. 2 to 4 are designated by the same reference numerals as used in FIGS. 2 to 4, and explanation thereof is omitted. In FIG. 5, the drive device 15 (such as a linear motor) is provided in an atmospheric environment, and a non-contacting seal device (a differential exhausting or vacuum seal device) 25 is provided in the passage 3a in which the connecting member 16 connecting the stage device 11 and the drive device 15 extends. The non-contacting seal device 25 provides a seal between the first vacuum chamber 1 and the atmospheric environment. The non-contacting seal device 25 comprises a plurality of (three in this embodiment) vacuum grooves 26 formed in an inner circumferential surface of the wall 6 in the passage 3a. The vacuum grooves 26 are individually connected to evacuation lines. The vacuum grooves 26 are evacuated through the evacuation lines so as to produce individual vacuum pressures P3, P4 and P5 in the vacuum grooves 26 so that the relationship P0>P3>P4>P5>P1 is established (if P0, P3, P4, P5 and P1 are replaced by the corresponding degrees of vacuum DV0, DV3, DV4, DV5 and DV1, the relationship DV0<DV3<DV4<DV5<DV1 is established). In this arrangement, there is no need to evacuate the second space 2a, and the apparatus can be reduced in size. Further, the non-contacting seal device 25 is employed, instead of the bellows type seal device 21 in FIG. 4. Therefore, the problems of a reaction force and vibrations produced by expansion and contraction of the bellows can be avoided.
In this arrangement, however, when the non-contacting seal device 25 stops operating, atmospheric pressure is introduced into the first vacuum chamber 1 through the passage 3a, so that the pressure in the first vacuum chamber 1 becomes substantially equal to atmospheric pressure. That is, the vacuum of the first vacuum chamber 1 cannot be maintained. Therefore, when the apparatus stops operating in the event of emergency, for example, a power failure, a vacuum must be reproduced in the first vacuum chamber 1a, and the time required for reproducing a vacuum becomes considerably long, depending on the characteristics of the gas flowing into the first vacuum chamber 1.
Therefore, a substrate processing apparatus as shown in FIG. 6 is proposed. The apparatus of FIG. 6 comprises a first space or vacuum chamber 1a in which the stage device 11 is provided, and a second space or chamber 7 (pressure: P7) in which the drive device 15 (such as a linear motor) is provided. The space 7 is separated from an ambient atmosphere by a cover 8 and from the first vacuum chamber 1a by the wall 6 and the non-contacting seal device (differential exhausting seal device) 25. The non-contacting seal device 25 is provided in the passage 3a in which the connecting member 16 connecting the stage device 11 and the drive device 15 extends. The non-contacting seal device 25 in FIG. 5 has the same structure and performs the same function as the non-contacting seal device 25 shown in FIG. 4. A plurality of (three in this embodiment) vacuum grooves 26 are formed in the inner circumferential surface of the wall 6 in the passage 4 and are individually connected to the evacuation lines L6-1, L6-2 and L6-3. The vacuum grooves 26 are evacuated so as to produce individual vacuum pressures P3, P4 and P5, which satisfy the relationship P7>P6-3>P6-2>P6-1>P1 (if P7, P3, P4, P5 and P1 are replaced by the corresponding degrees of vacuum DV7, DV3, DV4, DV5 and DV1, the relationship DV7<DV3<DV4<DV5<DV1 is established). In this arrangement, atmospheric pressure is not directly introduced into the first vacuum chamber 1, even when the non-contacting seal device 25 stops operating.
In the above-mentioned arrangements, the movable base 13 of the stage device 11 is movably supported by the rolling mechanism 14. Theoretically, it is impossible to prevent generation of dust in the rolling mechanism 14.
Therefore, in a substrate processing apparatus shown in FIG. 7, a stage device 31 having no rolling mechanism is provided. A movable base 33 of the stage device 31 is supported, on one side, by the connecting member 16, while the connecting member 16, and hence the movable base 33, are supported by using a non-contacting type guide element [such as a static bearing (an air bearing)] 35. The non-contacting type guide element 35 is provided in the passage 3a at a position adjacent to the non-contacting seal device 25 and on a side of the drive device 15. Thus, there is no problem of generation of dust. Further, because the non-contacting seal device 25 is used, it is possible to avoid generation of dust in a seal portion, and problems of a reaction force and vibrations produced by a bellows can also be avoided. In the arrangement of FIG. 7, the space in which the drive device 15 is placed is an atmospheric environment. The movable base 33 of the stage device 31 is supported on one side, but this does not limit the arrangement of FIG. 7. Incidentally, in the arrangement of FIG. 7, relative horizontal positions of a reflecting mirror 41 provided on the movable base 33 on which the substrate S is loaded and a reflecting mirror 42 provided on a side of the electron beam generating column 17 are measured by a laser interferometer 43. The pressure relationship in this arrangement is P0<PB>P6-3>P6-2>P6-1>P1, wherein PB represents an internal pressure of the static bearing 35, and P6-3, P6-2 and P6-1 represent the pressures in the vacuum grooves 26 of the non-contacting seal device 25 which are evacuated through the evacuation lines. If P0, PB, P6-3, P6-2, P6-1 and P1 are replaced by the corresponding degrees of vacuum DV0, DVB, DB6-3, DB6-2, DV6-1 and DV1, the relationship DV1>DV6-1>DV6-2>DV6-3>DVB<DV0 is established. DVB represents the degree of vacuum of the static bearing 35.
In the arrangement of FIG. 7, only one vacuum chamber 1 is provided. Therefore, a vacuum system having a simple construction can be used, and the size of the apparatus can be reduced. However, as in the case of FIG. 5, when the non-contacting seal device 25 stops operating, atmospheric pressure is inevitably introduced into the first vacuum chamber 1 through the passage 4 and therefore, the pressure in the first vacuum chamber 1 becomes substantially equal to atmospheric pressure. That is, the vacuum of the first vacuum chamber 1 cannot be maintained. Consequently, a considerable amount of time is required for reproducing a vacuum.
In a substrate processing apparatus shown in FIG. 8, differing from the apparatus of FIG. 7, a space in which the drive device 15 (such as a linear motor) is provided is defined, by the cover 8, as the second space or chamber 7 which is separated from an ambient atmosphere by the cover 8 and from the first vacuum chamber 1 by the wall 6 and the non-contacting seal device 25. In this apparatus, the pressure relationship is P7<PB>P6-3>P6-2>P6-1>P1. If P7, PB, P6-3, P6-2, P5-1 and P1 are replaced by the corresponding degrees of vacuum DV7, DVB, DV6-3, DV6-2, DV6-1 and DV1, the relationship DV1>DV6-1>DV6-2>DV6-3>DVB<DV7 is established.
The drive device 15 is not limited to a linear motor. For example, a cylinder device may be used. When a cylinder device is used as the drive device 15, care must be taken to avoid 1) leakage of a differential fluid from a seal portion (a release of gas), 2) generation of dust in the seal portion and 3) a temperature change caused by compression and expansion of a fluid.
In a conventional technique shown in FIG. 2, a device (such as a drive device) which causes a release of gas, and generation of dust and heat, is provided in the second space or vacuum chamber 2a, while a substrate is provided in the first space or vacuum chamber 1a. A pressure differential between the first vacuum chamber 1a and the second vacuum chamber 2a is determined so as to satisfy the relationship P1 <P2 (In terms of a degree of vacuum DV, DV1>DV2). With respect to the reason for this determination, it is considered as follows. With respect to the first vacuum chamber 1a, a high degree of vacuum is required to be produced, because a clean environment must be formed in a space in which a substrate is provided. With respect to the second vacuum chamber 2a in which a device that causes a deterioration in the second vacuum chamber 2a is provided, a release of gas from the device cannot be avoided, and cleanliness of the second vacuum chamber 2 is not as highly necessary as compared to the first vacuum chamber 1a. Therefore, the vacuum of the second vacuum chamber 2a may be lower than that of the first vacuum chamber 1a. 
However, leakage of gas inevitably occurs between two chambers having different pressures. That is, there is a possibility that part of a gas generated in the second vacuum chamber 2a flows into the first vacuum chamber 1a, which is required to be clean.
Further, in practice, there is a problem of a reverse flow or diffusion of gas derived from an oil component from an oil-sealed rotary vacuum pump, an oil component remaining in parts or ducts of a vacuum system, and a lubricant used for the vacuum pump. When the above pressure relationship P1<P2 (in terms of a degree of vacuum DV, DV2<DV1) is established in the apparatus of FIG. 2, a gas which has been introduced into the second vacuum chamber 2a due to the above-mentioned reverse flow or diffusion is further introduced from the second vacuum chamber 2a into the first vacuum chamber 1a. 
In a conventional technique shown in FIG. 6, the non-contacting seal device (differential exhausting seal device) 25 is employed as a seal device. When a gap between the connecting member 16 and the inner circumferential surface of the wall 6 defining the passage 3a is indicated by g0, the value of g0 is about 5 to 50 μm. From the viewpoint of reducing a load on the vacuum system, the value of g0 should be minimized. This means that a sealing performance changes due to variations in the value of go resulting from pressure variations (in a range between atmospheric pressure and a vacuum pressure) in the vacuum chamber. To prevent such variations in the value of go, it is necessary to form a rigid structure by, for example, increasing a wall-thickness of the housing 3 defining the vacuum chamber. However, this leads to a problem, such as a large weight of the apparatus.
The same problem is encountered in the apparatus shown in FIG. 8. Further, in the apparatus of FIG. 8 in which the non-contacting type guide element 35 is used, a guiding performance also changes due to variations in the value of gap g0. Therefore, a problem occurs, such that orthogonality of the movable base 33 of the stage device 31 is impaired, or the substrate's surface is vertically displaced.
FIG. 9 indicates the pressure relationship established in the apparatus in which the differential exhausting seal device 25 (of a type having three vacuum grooves) is provided between the first vacuum chamber la and the second chamber or space 7. P7 may be atmospheric pressure. The gas flowing towards the first vacuum chamber 1a (in which a substrate is processed) due to a pressure differential between the first vacuum chamber 1a and the second chamber or space 7 is sucked through the three vacuum grooves, thus preventing the gas from flowing into the first vacuum chamber 1a. Normally, the pressure distribution (relationship) is P7>P6-3>P6-2>P6-1>P1. Therefore, a slight amount of gas flows from a region under pressure P5 into the first vacuum chamber 1a under pressure P1. It is most undesirable to allow a reverse flow or diffusion of gas derived from an oil component from an oil-sealed rotary vacuum pump, an oil component remaining in parts or ducts of a vacuum system, and a lubricant used for the vacuum pump. In many cases, a high-vacuum pump having a large volume is used so that the first vacuum chamber la has the highest degree of vacuum (P1 becomes the lowest pressure). However, this high-vacuum pump causes a reverse flow of an oil component from the oil-sealed rotary vacuum pump for the vacuum groove of the pressure P6-1, an oil component remaining in parts or ducts of the vacuum system, and a vapor of a lubricant used for the vacuum pump.